1. Field of the Invention
An aspect of the present invention relates to a method and apparatus for recording and/or reproducing holographic data and a holographic information storage medium, and more particularly, to a microholography-type method and apparatus for recording and/or reproducing holographic data in which the amount of aberration is reduced, and a holographic information storage medium.
2. Description of the Related Art
Information storage technology using holograms has been recently highlighted. In the information storage method using holograms, information is stored in the form of an optical interference pattern in an inorganic crystal or polymer material sensitive to light. The optical interference pattern is formed by using two coherent laser beams. That is, an interference pattern which is formed when a reference beam and a signal beam having different paths interfere with each other causes chemical or physical changes in a photosensitive storage medium, thereby recording the interference pattern in the medium.
In order to reproduce information from the thus recorded interference pattern, a reference beam similar to the beam used when the information is recorded is emitted to the interference pattern recorded in the storage medium. This causes diffraction by the interference pattern, thereby restoring a signal beam and reproducing the information.
This hologram information storage technology includes a volume holographic method in which information is recorded and/or reproduced in units of pages by using volume holography, and a microholographic method in which information is recorded and/or reproduced in units of single bits by using microholography. Although the volume holographic method has an advantage in that a large amount of information can be processed at the same time, it is difficult for the method to be commercialized as an information storage apparatus for general consumers because the optical system needs to be adjusted very precisely.
In the microholographic method, two condensed light beams are made to interfere with each other at the focal point, and by moving this interference pattern on the plane of a storage medium, a plurality of patterns are recorded to form a recording layer. By superimposing the recording layers in a depth direction of the storage medium, patterns are recorded, thereby recording information in a 3-dimensional (3D) manner.
A conventional microholography-type apparatus for recording and/or reproducing holographic information uses an optical system having identical numerical apertures for a signal beam and a reference beam so that the signal beam and the reference beam have the same spot size. However, when the numerical aperture of the optical system is increased in order to increase a recording capacity, it becomes very sensitive to movements, such as tilting, and the aberration to be compensated becomes too big, thereby complicating the optical system and increasing manufacturing costs.